The human auditory system has evolved accurately to locate sounds that occur within the environment of the listener. The accuracy is thought to be derived primarily from two calculations carried out by the brain. The first is an analysis of the initial sound arrival and arrival of near reflections (the direct sound or head portion of the sound) which normally help to locate a sound; the second is an analysis of the reverberant tail portion of a sound which helps to provide an “environmental feel” to the sound. Of course, subtle differences between the sounds received at each ear are also highly relevant, especially upon the receipt of the direct sound and early reflections.
For example, in FIG. 1, there is illustrated a speaker 1 and listener 2 in a room environment. Taking the case of a single ear 3, the listener 2 receives a direct sound 4 from the speaker and a number of reflections 5, 6, and 7. It will be noted that the arrangement of FIG. 1 essentially shows a two dimensional sectional view and reflections off the floors or the ceilings are not shown. Further, the audio signal to only one ear is illustrated.
Often it is desirable to simulate the natural process of sound around a listener. For example, the listener, listening to a set of headphones, can be provided with an “out of head” experience of sounds appearing to emanate from an external environment. This can be achieved through the known process of determining an impulse response function for each ear for each sound and convolving the impulse response functions with a corresponding audio signal so as to produce the environmental effect of locating the sound in the external environment.